Corals belong to the phylum Cnidaria, a group that includes jellyfish and sea anemones. While true corals (Scleractinians) typically cause mild or unnoticeable stings, the most painful injuries often come from other reef organisms. All Cnidarians possess specialized stinging cells called cnidocytes, which contain a capsule called a nematocyst. Upon contact, this microscopic structure fires a venom-laden thread into the skin, causing a reaction.
Identifying the Stinging Culprit
The organism responsible for the most intense “coral stings” is Fire Coral (genus Millepora). This hydrozoan is not a true hard coral; it is more closely related to hydroids. However, it constructs a hard, calcareous skeleton, leading to its common misidentification.
The sting mechanism relies on thousands of nematocysts housed in specialized polyps called dactylozooids. These stinging cells discharge venom when triggered by touch, causing the characteristic fiery sensation.
Fire Coral is common in tropical and subtropical waters, often displaying yellow-green or brownish coloration, though blue or orange shades also occur. Its appearance can be branching, plate-like, or encrusting. A key identifier is a fuzzy or hairy appearance due to the fine, stinging polyps protruding from the skeleton, differentiating it from the smooth texture of true corals.
Immediate Symptoms and First Aid
Contact with Fire Coral causes immediate, burning pain that may last several hours. A red rash with raised welts or vesicles usually appears within minutes to hours. This localized reaction is caused by the venom, which has dermonecrotic (tissue-damaging) effects.
Immediate first aid focuses on neutralizing and removing unfired nematocysts. First, rinse the affected area thoroughly with seawater; fresh water can cause remaining nematocysts to discharge more venom and increase pain. Next, apply a mild acidic solution, such as household white vinegar, for a few minutes. Vinegar stabilizes the unfired stinging cells, preventing further venom injection.
After vinegar treatment, carefully remove any remaining nematocysts or coral fragments. Use adhesive tape to gently lift off the stinging cells, or apply shaving cream and gently shave the area with a dull edge. Once removed, keep the area clean and dry, and apply hydrocortisone cream to manage itching. If symptoms include signs of an allergic reaction, such as shortness of breath or facial swelling, seek immediate medical attention.
The Threat of Coral Cuts and Infection
Contact with non-venomous, true hard corals poses a risk because their sharp, calcified skeletons can cause cuts and deep abrasions. The primary danger is the introduction of foreign marine matter into the open wound, not venom. Coral skeletons and surrounding water harbor microorganisms and debris that can become embedded in the tissue.
This contamination can lead to a secondary bacterial infection, sometimes called “coral poisoning.” The risk of aggressive infections is increased because marine bacteria, such as Vibrio species, thrive in these wounds. Thorough cleaning is paramount: the cut should be scrubbed with soap and water and flushed with fresh water to remove all debris. Monitor the wound for signs of infection (increasing redness, swelling, pus, or fever), which require evaluation for antibiotic treatment.